DESCRIPTION (Verbatim from Applicant's Abstract): The goal of this proposal is to explore the development of a combined microCT/PET scanner for mouse imaging. Our interest is in ultimately using this technology for high throughput in vivo screening studies in functional genomics and in drug development, although there are many additional applications for a noninvasive imaging tool that provides both anatomical and functional data. The high resolution anatomical images provided by CT will enable better interpretation of the PET signal, and also permits improved quantification of the PET studies by objectively guiding organ and region of interest selection. In addition, the CT data provides a way to estimate partial volume correction and attenuation correction of the PET data. This proposal represents the initial technology development for a microCT/PET system. We have previously developed a high resolution microPET scanner. this proposal therefore focuses on the development and optimization of a table-top CT scanner, and its integration with existing microPET detectors. We propose to use a state-of-the-art amorphous selenium flat panel x-ray detector, in conjunction with a microfocus x-ray tube to reach a reconstructed CT resolution of 100-200 microns. In this proposal we will fully characterize the x-ray- tube and detector, and optimize the x-ray spectrum and system geometry for mouse imaging. We will pay close attention to the trade-off between resolution, signal-to-noise and radiation dose to the mouse. Appropriate phantoms will be developed to allow quantitative assessment of image quality. Different data collection and reconstruction schemes for 3D whole body mouse imaging will be explored through measurement and simulation, and the performance of the microCT system evaluated. We will study cross-talk between a microPET detector and the CT system and look at shielding requirements to mount the PET detectors coplanar with the CT system, or, axially displaced from the CT system. Finally, we will integrate a small number of microPET detectors with the CT system and acquire initial PET/CT studies in phantoms and mice.